> 1729 is known as Ramanujan number or Hardy–Ramanujan number, named after an anecdote of the British mathematician G. H. Hardy when he visited Indian mathematician Srinivasa Ramanujan who was ill in hospital. In their conversation, Hardy stated that the number 1729 from a taxicab he rode was a "dull" number and "hopefully it is not unfavourable omen", but Ramanujan remarked that "it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways". This conversation led to the definition of the taxicab number as the smallest integer that can be expressed as a sum of two positive cubes in a given number of distinct ways. 1729 is the second taxicab number, expressed as 1³+12³=9³+10³.

When I explain this to people, I say: given Rubik's cubes of size 1x1x1, 2x2x2, 3x3x3,..., 15x15x15, and a scale. Make the scale in balance with something on it.

The solution is to put 1x1x1 and 12x12x12 on one side and 9x9x9 and 10x10x10 on the other.